1. Field of the Invention
The present invention relates to a sheet comprising an olefin thermoplastic elastomer having excellent light resistance and thermal aging resistance, a laminate comprising said sheet and a use thereof. More precisely, the invention relates to a sheet comprising an olefin thermoplastic elastomer having excellent duration properties, particularly light resistance or the like, which is excellent in external appearance and touch or the like and which may be substituted for plasticized polyvinyl chloride material; a laminate constituting said sheet; and an internal finish material for automobile constituting said sheet or laminate.
2. Background Information
Thermoplastic elastomers have found wide application in industrial products including automobile parts, electric appliance parts and sundry goods since the time consuming vulcanization step is not required in the productions of them and they can be processed using a conventional molding machine for a thermoplastic resin.
On the other hand, moldings of improved quality have hitherto been known which were produced by laminating a skin material onto a molded thermoplastic resin to impart improved external appearance and soft touch. As the skin material, for example, a plasticized polyvinyl chloride material lined with a foamed layer of polyolefin or polyurethane in order to impart cushioning properties has been used.
The polyvinyl chloride skin material, however, has the problem that it has a large specific gravity and an inferior light resistance. Therefore its surface appearance is significantly deteriorated when used as a skin material for an automobile part which is exposed to direct sun light. In addition, since it is plasticized by containing a large amount of plasticizer, it has a problem in that the windshield and the like become fogged up due to the plasticizer when used as an internal finish skin material for automobile.
Furthermore, since polyvinyl chloride generates hydrogen chloride gas upon combustion due to its chemical structure, it has the added problems in that its incineration after use should not be permitted from an environmental viewpoint, and that it tends to erode various processing apparatuses.
In order to solve the above described problems, it was proposed to produce a skin material by using an olefin thermoplastic elastomer comprising ethylene-.alpha.-olefin-unconjugated diene copolymer rubber as the rubber component (JP-A-4-73112).
However when ethylidenenorbornene was used as the unconjugated diene, the properties of the product deteriorated within a short period upon exposure to light.
When dicyclopentadiene is used as the unconjugated diene, deterioration of the properties within a short period is less significant (JP-A-5-279524), but there is still the problem that the thermal aging resistance of the product was not sufficient. Therefore, when a thermoplastic elastomer sheet containing one of these unconjugated dienes is applied for a use in which light resistance is particularly required, such as a skin material for the instrument panel of automobile, a large amount of light stabilizer must be used in order to prevent light aging. As the result, problems arose because the sheet became dirty due to the light stabilizer deposited on the surface of the sheet or the windshield was fogged up by sublimed light stabilizer.
The object of the present invention, therefore, is to solve these problems of the conventional art and to provide a sheet comprising an olefin thermoplastic elastomer having excellent light resistant and heat resistant properties, a laminate comprising said sheet and an internal finish material for an automobile comprising said sheet or laminate.
After extensive research toward solving these problems, the present inventors have found that the light deterioration and the heat deterioration are less significant when an olefin thermoplastic elastomer is produced using an olefin polymer rubber free from unconjugated diene and using particular amounts of a specific cross-linking agent and a specific cross-linking aid. The present invention has been completed on the basis of such findings and further improvement.